1. Field of the Invention
The present invention pertains to a hydraulic fracturing process for subterranean hydrocarbon producing formations which includes injection of a cold liquid into the formation to reduce the earth stresses and to control the extent of the fracture within the desired mineral producing zone.
2. Background
When a relatively cold fluid, such as water, is injected into a relatively warm subterranean hydrocarbon bearing reservoir an ever increasing region of cooled rock is established around the injection well and results in the reduction in stresses in the rock which may be on the order of several hundred pounds per square inch (psi). This reduction in stresses in the rock matrix may be utilized to extend hydraulic fractures to enhance the recovery of liquid and gaseous hydrocarbon substances present in the formation to be produced.
Discussions of the effects of thermoelastic stresses in earth formations resulting from the injection of relatively cold liquids into relatively warm formations are discussed in papers published by T. K. Perkins and J. A. Gonzalez entitled "Changes in Earth Stresses Around a Wellbore Caused by Radially Symmetrical Pressure and Temperature Gradients", Society of Petroleum Engineers Journal, April, 1984, and "The Effect of Thermoelastic Stresses on Injection Well Fracturing", Society of Petroleum Engineers Journal, February, 1985. These papers present methods to determine the effect of the injection of large volumes of liquid into a subterranean earth formation and methods for calculating the thermoelastic stresses and hydraulic fracturing pressures required to achieve a hydraulic fracture. At least some of the assumptions made in the abovementioned publications can be utilized in dealing with fracturing lightly consolidated formations such as the type found in the West Sak Oil Field in Alaska. It is particularly important in developing fields which have relatively low well productivity as determined by conventional fracturing methods to improve productivity by enhancing the width and size of the fracture without the chance of extending the fracture outside of the mineral bearing formation or zone which is desired to be produced.
Conventional hydraulic fracturing, particularly in lightly consolidated formations, is difficult to control as regards the extent of the fracture. Moreover, in lightly consolidated formations, such as the abovementioned oil field, relatively large quantities of fine solid particles are usually carried with the flowing oil stream being produced. These formation particles are carried into a propped hydraulic fracture and tend to significantly reduce fracture conductivity. To prevent the embedment or saturation of the fracture proppant by these relatively fine particles, smaller sizes of proppant particles might be used. However, the use of smaller proppant particles also requires wider fractures to achieve the fracture conductivity required to make the well completion economical. Under these conditions, the use of conventional hydraulic fracturing processes to achieve wide fractures greatly increases the chance of fracturing beyond the desired formation boundaries.
It is an object of the present invention to improve the productivity of hydrocarbon bearing reservoirs which may be damaged or degraded by uncontrolled hydraulic fractures. It is a further object of the present invention to provide an improved process for hydraulically fracturing a hydrocarbon bearing formation, including formations which are lightly consolidated, so as to increase well productivity. These objects, as well as additional objects obtained by the present invention, will be further appreciated by those skilled in the art.